The effects of ionizing and ultra-violet radiation on nucleic acids and proteins and their constituents are being studied. The modification of radiation damage in DNA by cancer chemotherapy agents of the intercalating and alkylating types is of interest, since such information may be useful in radiation therapy. The present report includes electron spin resonance (e.s.r.) studies of spin-trapped radicals produced by gamma-irradiation of polycrystalline amino acids, peptides, nuclei acid bases, nucleosides and their 5-halosubstituted derivatives. The UV-photolysis of aliphatic and aromatic peptides in aqueous solutions was investigted by spin-trapping. The free radicals in gamma-irradiated single crystals of glutaric acid were studied in the temperature range from 77 degrees K to 300 degrees K.